Absolutely YES! Many Tungsten and tungsten carbide rings have Cobalt in them. The alloy containing Cobalt is easier to procure and tungsten rings containing Cobalt are being commonly sold. However, tungsten rings containing Cobalt will develop a negative reaction to your skin. After a short time period the ring will develop oxidation spots that cannot be removed or polished out. This is due to the Cobalt reacting to the human body. You can easily prevent this from happening by purchasing one of our Cobalt free tungsten carbide rings.